This invention relates generally to agents and methods for the prevention and treatment of retroviral disease and more specifically to an outer envelope free viral preparation for use in vaccination against and immunotherapy of Human Immunodeficiency Virus.
Acquired Immune Deficiency Syndrome, also known as AIDS, has been described as a modern plague. In the seven years since its first description in 1981, it has claimed almost 60,000 victims, and accounted for over 32,000 deaths in the United States alone. However, the true impact of the disease has yet to be felt. The virus may remain latent in infected individuals for five or more years before symptoms appear. Many Americans may unknowingly be infected and capable of infecting others who might come into contact with their body fluids. Thus, if unchecked, the personal, social and economic impact of AIDS will be enormous.
The causative agent of AIDS is the retrovirus Human Immunodeficiency Virus (HIV). Retroviruses are distinguished by the fact that their genetic material, which is RNA, encodes the information for viral replication. Upon infection of a host cell, it acts as a template for the transcription to DNA, catalyzed by an enzyme called reverse transcriptase. The DNA so produced enters the cell nucleus where it is integrated into the host DNA as a provirus. When properly activated, the retroviral-derived DNA is transcribed and translated to produce RNA containing virions which are then released from the cell by a budding process.
Certain viruses, including retroviruses, may remain in a latent state for months or years before they are activated and virions are produced. Although asymptomatic, a host may nonetheless harbor the virus in a proviral form, thus being potentially at risk of disease and of infecting others.
When an individual becomes infected with HIV, the virus preferentially attaches to and enters a particular class of cells termed T4 lymphocytes, characterized by the presence of a cell surface marker termed CD4. These white blood cells play an integral role in the immune system, functioning as critical components of both the humoral and cellular immune response. Much of the deleterious effect of HIV can be attributed to the functional depression or destruction of T4 lymphocytes.
The intact HIV virion is roughly spherical and is approximately 110 nm in diameter. The virion has an outer membrane covered with knobs or spikes made up of glycoprotein, gp160/120. In addition, there exists a transmembrane protein termed gp41. Inside the virion are two structural proteins: an outer shell composed of the phosphoprotein p17 and an inner nucleoid or central core made up of the phosphoprotein, p24. The viral RNA is present inside the core along with two copies of the reverse transcriptase enzyme, p66/51, which is necessary for the synthesis of viral DNA from the RNA template. A schematic model of HIV is presented in FIG. 1.
As shown in FIG. 2, the HIV RNA genome encodes three major structural genes: gag, pol and env, which are flanked at either end by long terminal repeat (LTR) sequences. The gag gene codes for the group-specific core proteins, p55, p39, p24, p17 and p15. The pol genes code for the reverse transcriptase p66/p51 and the protease p31. The env genes encode the outer envelope glycoprotein gp120 and its precursor gp160 and the transmembrane glycoprotein gp41. Some of the genes tend to be highly variable, particularly the env genes. In addition, there are five other genes, not shared by other retroviruses, which are either involved in transcriptional or translational regulation or encode other structural proteins. The entire HIV genome has now been sequenced. See Ratner et al. Nature 313:277 (1985) which is incorporated herein by reference.
The HIV attaches to host cells by an interaction of the envelope glycoproteins with a cell surface receptor. It appears that when HIV makes contact with a T4 cell, gp120 interacts with the CD4 receptor. The viral envelope is then fused with the cell membrane and the inner core of the virus enters the infected cell where the transcription of RNA into a DNA provirus is catalyzed by reverse transcriptase. The provirus may remain in the cell in a latent form for some months or years, during which time the infected individual is asymptomatic. However, if the virus is later activated causing viral replication and immunosuppression the individual will than be susceptible to the opportunistic infections, including cancer, associated with AIDS. Other human retroviruses have outer envelope proteins.
As yet, no vaccine or treatment is known which is effective against the AIDS syndrome. Attempts to develop vaccines have thus far failed. Certain antibodies reactive with HIV, notably anti-gp160/120 and virus neutralizing antibodies, are present at high levels throughout both the asymptomatic and symptomatic phases of the HIV infection, suggesting that rather than playing a protective role, such antibodies may in fact promote the attachment and penetration of the virus into the host cell.
There thus exists a need for effective agents to be used in the prevention and therapy of retroviral infections, particularly those attributed to HIV. The present invention satisfies these needs and provides related advantages as well.